A Russian drone violated Romania's airspace during night-time attacks on neighbouring Ukraine, the Nato member reported on Sunday.
Romania’s ministry of defence has now urged Moscow to stop what it described as an escalation, AP has reported.
The incident happened as Russia carried out attacks on "civilian targets and port infrastructure" across the River Danube in Ukraine.
Romania deployed F-16 warplanes to monitor its airspace, and Nato allies were kept informed, the ministry said.
Romanian emergency authorities also issued text alerts to residents of two eastern regions.
Preliminary data indicates there may be an "impact zone" in an uninhabited area near the Romanian village of Periprava, the ministry said. It added that an investigation is under way.
Since Russia invaded Ukraine in February 2022, Romania has confirmed drone fragments on its territory on several occasions and as recently as July this year.
The Romanian Defence Ministry strongly condemned the Russian attacks on Ukraine, calling them "unjustified and in serious contradiction with the norms of international law".
NATO condemns the overnight Russian airspace violation into Romanian airspace. While we have no information indicating an intentional attack by Russia against Allies, these acts are irresponsible and potentially dangerous.
— Mircea Geoana (@Mircea_Geoana) September 8, 2024
Mircea Geoana, Nato's outgoing deputy secretary-general and Romania's former top diplomat, said the military alliance also condemned Russia's violation of Romanian airspace.
"While we have no information indicating an intentional attack by Russia against Allies, these acts are irresponsible and potentially dangerous," he tweeted.
Meanwhile, in Ukraine, two civilians were killed and four others, including two children, injured in a night-time Russian air strike on the northern city of Sumy, the regional military administration reported.
In the Kharkiv region further east, overnight shelling killed two elderly women, according to local governor Oleh Syniehubov.
During the night, Ukrainian air defences shot down one of four cruise missiles and 15 of 23 Iranian-made Shahed drones launched by Russia, Ukraine's air force reported.
It added that none of the cruise missiles had hit targets.
Later on Sunday, three women were killed when Russian forces shelled a village in the eastern Donetsk region, governor Vadym Filashkin reported on the Telegram messaging app.
Elsewhere in the province, rescue teams pulled the bodies of two men from the rubble of a hotel destroyed on Saturday evening in a Russian air strike, according to Ukraine's state emergency service.
